Thermoplastic elastomer compositions

ABSTRACT

A thermoplastic elastomer composition prepared by partially crosslinking a composition comprising the following components (A), (B), (C) and (D): 
     (A) 10-40% by weight of an ethylene/α-olefin copolymer prepared by copolymerizing ethylene and an α-olefin having 3 to 12 carbon atoms in the presence of a catalyst comprising a solid component and an organoaluminum compound which solid component contains at least magnesium and titanium, said ethylene/α-olefin copolymer having the following properties (I) to (IV): 
     (I) Melt index: 0.01-50 g/10 min 
     (II) Density: 0.860-0.910 g/cm 3   
     (III) Maximum peak temperature as measured according to a differential scanning calorimetry (DSC): not lower than 100° C. 
     (IV) Insolubles in boiling n-hexane: not less than 10 wt. % 
     (B) 15-35% by weight of a propylene polymer; 
     (C) 10-40% by weight of an ethylene/α-olefin copolymer rubber; and 
     (D) 10-40% by weight of an ethylene/unsaturated monocarboxylic acid ester copolymer in which the carboxylate unit content is 2-10 mol %.

BACKGROUND OF THE INVENTION

The present invention relates to a novel thermoplastic elastomer composition superior in fluidity and external appearance of molded articles. More particularly, it is concerned with a thermoplastic elastomer composition obtained by partially cross-linking a composition of (A) an extremely low density ethylene copolymer prepared by copolymerizing ethylene and an α-olefin in the presence of a specific catalyst, (B) a propylene polymer, (C) an ethylene/α-olefin copolymer rubber and (D) an ethylene/unsaturated monocarboxylic acid ester copolymer, the said thermoplastic elastomer composition being superior in fluidity, external appearance of molded articles and resistance to heat and oil, and being small in permanent set.

As thermoplastic polyolefin elastomers there are known compositions comprising crystalline polyolefins such as polyethylene and polypropylene as hard segments and amorphous copolymer rubbers such as ethylene/propylene copolymer rubber (EPR) and ethylene/propylene/non-conjugated diene copolymer rubber (EPDM) as soft segments, as well as compositions obtained by partially crosslinking the above compositions. It is also known to prepare hard and soft segments according to a multi-stage polymerization process. And by changing the proportions of those segments there are obtained various grades of products ranging from one superior in flexibility up to one having rigidity.

Products of the flexible grade are attracting great attention because they can be applied as rubbery materials widely to such uses as automobile parts, hoses, electric wire coating and packing. In preparing such flexible grade of products it is necessary to increase the proportion of a soft segment (e.g. EPR or EPDM) and decrease that of a hard segment (e.g. polyethylene or polypropylene) in order to impart rubbery flexibility thereto.

However, such soft segments as EPR and EPDM are poor in tensile strength and inferior in resistance to heat and oil and also inferior in fluidity. Consequently, flexible, thermoplastic elastomer compositions containing large amounts of such soft segments also have the above-mentioned drawback and cannot be applied to a wide variety of uses. Increasing the hard segment proportion to remedy these problems will result in loss of flexibility, deterioration of physical properties such as permanent set and consequent impairment of the function as a flexible, thermoplastic elastomer.

Moreover, in preparing a product of the flexible grade, it is necessary to carry out polymerizations separately for hard and soft segments, thus resulting in that not only the polymerization apparatus becomes very complicated in structure but also it is very difficult to control the properties and proportion of each segment in each polymerization stage and a defective product sometimes occurs at the time of changeover from one to another grade. Further, the recovery of the resulting polymer is also very difficult because a large amount of a rubbery component is contained therein.

Thus, a lot of problems remain to be solved in order to obtain a flexible, thermoplastic elastomer of good quality.

SUMMARY OF THE INVENTION

It is the object of the present invention to overcome the above-mentioned problems of the prior art and provide a highly flexible, thermoplastic elastomer composition having superior performance.

More specifically, the present invention resides in a thermoplastic elastomer composition obtained by partially crosslinking a composition comprising the following components (A), (B), (C) and (D): (A) 10-40% by weight of an ethylene/α-olefin copolymer prepared by copolymerizing ethylene and an α-olefin having 3 to 12 carbon atoms in the presence of a catalyst comprising a solid component and an organoaluminum compound which solid component contains at least magnesium and titanium, said ethylene/α-olefin copolymer having the following properties (I) to (IV):

(I) Melt index: 0.01-50 g/10 min

(II) Density: 0.860-0.910 g/cm³

(III) Maximum peak: temperature as measured according to a differential scanning calorimetry (DSC): not lower than 100° C.

(IV) Insolubles in boiling n-hexane: not less than 10 wt. %

(B) 15-35% by weight of a propylene polymer,

(C) 10-40% by weight of an ethylene/α-olefin copolymer rubber, and

(D) 10-40% by weight of an ethylene/unsaturated monocarboxylic acid ester copolymer in which the carboxylate unit content is 2-10 mol %.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS (1) Ethylene/α-Olefin Copolymer (A)

In the ethylene/α-olefin copolymer (A) used in the present invention, the α-olefin to be copolymerized with ethylene is one having 3 to 12 carbon atoms. Examples are propylene, butene-1, 4-methylpentene-1, hexene-1, octene-1, decene-1 and dodecene-1. Particularly preferred are propylene, butene-1, 4-methylpentene-1 and hexene-1 which having 3 to 6 carbon atoms. Further, dienes such as, for example, butadiene and 1,4-hexadiene may be used as comonomers. It is preferable that the α-olefin content in the ethylene/α-olefin copolymer be in the range of 5 to 40 mol %.

The following description is provided about how to prepare the ethylene/α-olefin copolymer (A) used in the present invention.

The catalyst system used comprises a solid catalyst component and an organoaluminum compound, the solid catalyst component containing at least magnesium and titanium. For example, the solid catalyst component is obtained by supporting a titanium compound on an inorganic solid compound containing magnesium by a known method. Examples of magnesium-containing inorganic solid compounds include, in addition to metal magnesium, magnesium hydroxide, magnesium carbonate, magnesium oxide, magnesium chloride, as well as double salts, double oxides, carbonates, chlorides and hydroxides, which contain magnesium atom and a metal selected from silicon, aluminum and calcium, further, these inorganic solid compounds after treatment or reaction with oxygen-containing compounds, sulfur-containing compounds, aromatic hydrocarbons or halogen-containing substances.

As examples of the above oxygen-containing compounds are mentioned organic oxygen-containing compounds such as water, alcohols, phenols, ketones, aldehydes, carboxylic acids, esters, polysiloxanes and acid amides, as well as inorganic oxygen-containing compounds such as metal alkoxides and metal oxychlorides. As examples of the above sulfur-containing compounds are mentioned organic sulfur-containing compounds such as thiols, thio-esters and the like, inorganic sulfur-containing compounds such as sulfur dioxide, sulfur trioxide, sulfuric acid and the like. As examples of the above aromatic hydrocarbons are mentioned mono- and polycyclic aromatic hydrocarbons such as benzene, toluene, xylene, anthracene and phenanthrene. As examples of the above halogen-containing compounds are mentioned chlorine, hydrogen chloride, metal chlorides and organic halides.

To illustrate the titanium compound, mention may be made of halides, alkoxyhalides, alkoxides and halogenated oxides, of titanium. Tetravalent and trivalent titanium compounds are preferred. As tetravalent titanium compounds are preferred those represented by the general formula Ti(OR)_(n) X_(4-n) wherein R is an alkyl, aryl or aralkyl group having 1 to 20 carbon atoms, X is a halogen atom and n is 0≦n≦4, such as, for example, titanium tetrachloride, titanium tetrabromide, titanium tetraiodide, monomethoxytrichlorotitanium, dimethoxydichlorotitanium, trimethoxymonochlorotitanium, tetramethoxytitanium, monoethoxytrichlorotitanium, diethoxydichlorotitanium, triethoxymonochlorotitanium, tetraethoxytitanium, monoisopropoxytrichlorotitanium, diisopropoxydichlorotitanium, triisopropoxymonochlorotitanium, tetraisopropoxytitanium, monobutoxytrichlorotitanium, dibutoxydichlorotitanium, monopentoxytrichlorotitanium, monophenoxytrichlorotitanium, diphenoxydichlorotitanium, triphenoxymonochlorotitanium and tetraphenoxytitanium. As examples of trivalent titanium compounds are mentioned titanium trihalides such as titanium tetrachloride and titanium tetrabromide reduced with hydrogen, aluminum, titanium or an organometallic compound of a Group I-III metal in the Periodic Table, as well as trivalent titanium compounds obtained by reducing tetravalent alkoxytitanium halides of the general formula Ti(OR)_(m) X_(4-m) with an organometallic compound of a Group I-III metal in the Periodic Table in which formula R is an alkyl, aryl or aralkyl group having 1 to 20 carbon atoms, X is a halogen atom and m is 0<m<4. Tetravalent titanium compounds are particularly preferred.

As preferred examples of catalyst systems are mentioned combinations of organoaluminum compounds with such solid catalyst components as MgO-RX-TiCl₄ (Japanese Patent Publication No. 3514/1976), Mg-SiCl₄ ROH-TiCL₄ (Japanese Patent Publication No. 23864/1975), MgCl₂ -Al(OR)₃ -TiCl₄ (Japanese Patent Publication Nos. 152/1976 and 15111/1977), MgCl₂ -SiCl₄ -ROH-TiCl₄ (Japanese Patent Laid Open No. 106581/1974), Mg(OOCR)₂ -AL(OR)₃ -TiCl₄ (Japanese Patent Publication No. 11710/1977), Mg-POCl₃ -TiCl₄ (Japanese Patent Publication No. 153/1976), MgCl₂ -AlOCl-TiCl₄ (Japanese Patent Publication No. 15316/1979) and MgCl₂ -Al(OR)_(n) X_(3-n) -Si(OR')_(m) X_(4-m) -TiCl₄ (Japanese Patent Laid Open No. 95909/1981), in which formulae R and R' are each an organic radical and X is a halogen atom.

As other examples of catalyst systems are mentioned combinations of organoaluminum compounds with reaction products as solid catalyst components obtained by the reaction of organomagnesium compounds such as so-called Grignard compounds with titanium compounds. Examples of organomagnesium compounds are those of the general formulae RMgX, R₂ Mg and RMg(OR) wherein R is an organic radical having 1 to 20 carbon atoms and X is a halogen atom, and ether complexes thereof, as well as modified compounds obtained by modifying these organomagnesium compounds with other organometallic compounds such as, for example, organosodium, organolithium, organopotassium, organoboron, organocalcium and organozinc.

More concrete examples of such catalyst systems are combinations of organoaluminum compounds with such solid catalyst components as RMgX-TiCl₄ (Japanese Patent Publication No. 39470/1975), RMgX-phenol-TiCl₄ (Japanese Patent Publication No. 12953/1979), RMgX halogenated phenol-TiCl₄ (Japanese Patent Publication No. 12954/1979) and RMgX-CO₂ -TiCl₄ (Japanese Patent Laid Open No. 73009/1982).

As still other examples of catalyst systems are mentioned combinations of organoaluminum compounds with solid products obtained by contacting such inorganic oxides as SiO₂ and Al₂ O₃ with the solid catalyst component containing at least magnesium and titanium. In addition to SiO₂ and Al₂ O₃ there also may be mentioned CaO, B₂ O₃ and SnO₂ as examples of inorganic oxides. Double oxides thereof are also employable without any trouble. For contacting these inorganic oxides with the solid catalyst component containing magnesium and titanium, there may be adopted a known method. For example, both may be reacted at a temperature of 20° to 400° C., preferably 50° to 300° C., usually for 5 minutes to 20 hours, in the presence or absence of an inert solvent, or both may be subjected to a co-pulverization treatment, or there may be adopted a suitable combination of these methods.

As more concrete examples of such catalyst systems, mention may be made of combination of organoaluminum compounds with SiO₂ -ROH-MgCl₂ -TiCl₄ (Japanese Patent Laid Open No. 47407/1981), SiO₂ -R-O-R'-MgO-AlCl₃ -TiCl₄ (Japanese Patent Laid Open No. 187305/1982) and SiO₂ MgCl₂ -Al(OR)₃ -TiCl₄ -Si(OR')₄ (Japanese Patent Laid Open No. 21405/1983) in which formulae R and R' are each a hydrocarbon radical.

In these catalyst systems the titanium compounds may be used as adducts with organocarboxylic acid esters, and the magnesium-containing inorganic solid compounds may be used after contact treatment with organic carboxylic acid esters. Moreover, the organoaluminum compounds may be used as adducts with organocarboxylic acid esters. Further, the catalyst systems may be prepared in the presence of organic carboxylic acid esters.

As organic carboxylic acid esters there may be used various aliphatic, alicyclic and aromatic carboxylic acid esters, preferably aromatic carboxylic acid esters having 7 to 12 carbon atoms. Examples are alkyl esters such as methyl and ethyl of benzoic, anisic and toluic acids.

As preferred examples of the organoaluminum compound to be combined with the solid catalyst component are mentioned those represented by the general formulae R₃ Al, R₂ AlX, RAlX₂, R₂ AlOR, RAl(OR)X and R₃ Al₂ X₃ wherein Rs, which may the same or different, are each an alkyl, aryl or aralkyl group having 1 to 20 carbon atoms, such as triethylaluminum, triisobutylaluminum, trihexylaluminum, trioctylaluminum, diethylaluminum chloride, diethylaluminum ethoxide, ethylaluminum sesquichloride, and mixtures thereof.

The amount of the organoaluminum compound used is not specially limited, but usually it is in the range of 0.1 to 1,000 mols per mol of the titanium compound.

The catalyst system exemplified above may be contacted with an α-olefin before its used in the polymerization reaction. By so doing, its polymerization activity can be greatly improved and a stabler operation is ensured as compared with the case where it is not so treated. In this case, various α-olefins are employable, but preferably those having 3 to 12 carbon atoms and more preferably those having 3 to 8 carbon atoms. Examples are propylene, butene-1, pentene-1, 4-methylpentene-1, hexene-1, octene-1, decene-1, dodecene-1, and mixtures thereof. The temperature and time of the contact between the catalyst system and α-olefin can be selected over a wide range, for example, 0°-200° C., preferably 0°-110° C., and 1 minute to 24 hours. The amount of the α-olefin to be contacted with the catalyst system can also be selected over a wide range, but usually it is desirable that the catalyst system be treated with 1 g to 50,000 g, preferably 5 g to 30,000 g, per gram of the solid catalyst component of the α-olefin and reacted with 1 g to 500 g per gram of the solid catalyst component of the α-olefin. The pressure in the contact treatment is not specially limited, but preferably it is in the range of -1 to 100 kg/cm².G.

In the α-olefin treatment, the catalyst system may be contacted with the α-olefin after combining the total amount of the organoaluminum compound used with the solid catalyst component, or the catalyst system may be contacted with the α-olefin after combining a part of the organoaluminum compound used with the solid catalyst component and the remaining portion of the organoaluminum compound may be added separately in the polymerization reaction. The contact treatment of the catalyst system with the α-olefin may be conducted in the presence of hydrogen gas or any other inert gas, e.g. nitrogen, argon or helium.

The polymerization reaction is carried out in the same manner as in the conventional olefin polymerization reaction using a Ziegler type catalyst. More particularly, the reaction is performed in a substantially oxygen- and water-free condition in vapor phase or in the presence of an inert solvent or using monomer per se as solvent. Olefin polymerizing conditions involve temperatures in the range of 20° to 300° C., preferably 40° to 200° C., and pressures in the range from normal pressure to 70 kg/cm².G, preferably 2 kg/cm².G or 60 kg/cm².G. The molecular weight can be adjusted to some extent by changing polymerization conditions such as polymerization temperature and catalyst mol ratio, but the addition of hydrogen into the polymerization system is more effective for this purpose. Of course, two or more multi-stage polymerization reactions involving different polymerization conditions such as different hydrogen concentrations and different polymerization temperatures can be carried out without any trouble.

The melt index (MI, according to JIS K 6760) of the ethylene/α-olefin copolymer (A) thus prepared is in the range of 0.01 to 50/10 min, preferably 0.1 to 20 g/10 min. Its density (according to JIS K 6760) is in the range of 0.860 to 0.910 g/cm³, preferably 0.870 to 0.905 g/cm³ and more preferably 0.870 to 0.900 g/cm³. Its maximum peak temperature (Tm) measured according to a differential scanning calorimetry (DSC) is not lower than 100° C., preferably not lower than 110° C. Its insolubles in boiling n-hexane are not less than 10 wt. %, preferably 20-95 wt. % and more preferably 20-90 wt. %.

If the melt index of the ethylene/α-olefin copolymer (A) is less than 0.01 g/10 min, the melt index of the thermoplastic elastomer composition will become too low, resulting in deterioration of its fluidity. And if it exceeds 50 g/10 min, the tensile strength will be reduced. A density thereof lower than 0.860 g/cm³ would result in lowering of tensile strength, surface stickiness of the composition and impairment of the appearance. A density of the copolymer exceeding 0.910 g/cm³ is not desirable, because it would cause deterioration of flexibility and transparency. A maximum peak temperature thereof as measured according to DSC of lower than 100° C. is not desirable, either, because it would result in lowering of tensile strength, surface stickiness of the composition and reduced resistance to heat and oil. If the proportion of insolubles in boiling n-hexane is smaller than 10 wt. %, the resulting composition will be reduced in tensile strength and become sticky on its surface, and thus such a proportion is undesirable.

(2) Propylene Polymer (B)

As examples of the propylene polymer (B) used in the present invention there are mentioned not only a homopolymer of propylene but also block and random copolymers of propylene and other comonomers. Preferred as the comonomers are α-olefins having 2 to 8 carbon atoms such as, for example, ethylene, butene-1, hexene-1, 4-methylpentene-1, and octene-1. Preferably, these comonomers are present in proportions not larger than 30 mol % in the copolymers.

The melt flow rate (MFR, according to JIS K 6758) of the propylene polymer is in the range of 0.01 to 100 g/10 min, preferably 0.1 to 50 g/10 min. If MFR is smaller than 0.01 g/10 min, it will be impossible to obtain a resin composition having good fluidity, and if MFR exceeds 100 g/10 min, it will result in reduced tensile strength and impact strength.

(3) Ethylene/α-Olefin Copolymer Rubber (C)

The ethylene/α-olefin copolymer rubber (C) used in the present invention is an ethylene/α-olefin copolymer rubber or an ethylene/α-olefin/non-conjugated diene copolymer rubber. These are amorphous copolymer.

In the ethylene/α-olefin copolymer rubber (C), examples of the α-olefin are α-olefins having 3 to 12 carbon atoms such as propylene, butene-1, pentene-1, 4-methylpentene-1, hexene-1 and octene-1, with propylene being particularly preferred.

Examples of the non-conjugated diene are 1,4-hexadiene, 1,6-octadiene, dicyclopentadiene, vinyl norbornene and ethylidene norbornene, with 1,4-hexadiene and ethylidene norbornene being preferred.

The ethylene/α-olefin copolymer rubber used in the invention has a Mooney viscosity (ML₁₊₄, 100° C.) of 10 to 95. A Mooney viscosity thereof lower than 10 is not desirable because it would result in reduced tensile strength or sticky surface of the thermoplastic elastomer composition. A Mooney viscosity of the copolymer rubber exceeding 95 is also undesirable because it will lead to deterioration in flowing property of the thermoplastic elastomer composition.

The ethylene/α-olefin copolymer (A) and the ethylene/α-olefin copolymer rubber (C), which are components of the thermoplastic elastomer composition of the present invention, are easily distinguishable from each other. Even if both are the same in point of the constituent monomers and density, the maximum peak temperature (Tm) is much higher in the component (A), while in the case of component (C), even if there is a maximum peak temperature (Tm) thereof, it is in the range of 30° to 50° C. at most. Also as to insolubles in boiling n-hexane, the component (C) does not contain such insolubles, or even if it contains such insolubles, the amount thereof is extremely small. The two components are also greatly different in point of how to prepare them. The component (A) is prepared using a catalyst which contains magnesium and titanium as previously noted, while the component (C) is usually prepared using a vanadium catalyst.

(4) Ethylene/Unsaturated Monocarboxylic Acid Ester Copolymer (D)

The carboxylate unit content of the ethylene/unsaturated monocarboxylic acid ester copolymer (D) used in the present invention is in the range of 2 to 10 mol %, preferably 3 go 10 mol %. A carboxylate unit content thereof exceeding 10 mol % would cause a lowering of tensile strength and create a surface stickiness of the elastomer, and a carboxylate unit content thereof lower than 2 mol % would cause deterioration of flexibility and increase in permanent set.

The melt index of the ethylene/unsaturated monocarboxylic acid ester copolymer may vary in wide range, but preferably it is in the range of 0.1 to 20 g/10 min.

The unsaturated monocarboxylic acid ester which is a comonomer of the copolymer may be derived from acrylic acid or methacrylic acid and an alcohol having 1 to 6 carbon atoms. Examples are methyl acrylate, ethyl acrylate, butyl acrylate, methyl methacrylate, ethyl methacrylate and the like.

(5) Composition Ratio (Mixing Ratio)

The composition ratios of the ethylene/α-olefin copolymer (A) [hereinafter referred to as component (A)], the propylene polymer (B) [hereinafter referred to as component (B)], the ethylene/α-olefin copolymer rubber (C) [hereinafter referred to as component (C)] and the ethylene/unsaturated carboxylic acid ester copolymer (D) [hereinafter referred to as component (D)] in the thermoplastic elastomer composition of the present invention are 10-40%, preferably 15-30%, by weight of component (A), 15-30%, preferably 20-30%, by weight of component (B), 10-40%, preferably 15-30%, by weight of component (C), and 10-40%, preferably 15-30%, by weight of component (D).

If the proportion of component (A) exceeds 40% by weight, the heat resistance and fluidity will be deteriorated, and if it is smaller than 10% by weight, the strength will be deteriorated.

If the proportion of component (B) exceeds 35% by weight, the flexibility will be deteriorated, and if it is smaller than 15% by weight, the fluidity and heat resistance will be deteriorated.

If the proportion of component (C) exceeds 40% by weight, the tensile strength and heat resistance will be deteriorated, and if it is smaller than 10% by weight, the flexibility and permanent elongation will be deteriorated.

If the proportion of component (D) exceeds 40% by weight, the flexibility and heat resistance will be deteriorated, and if it is smaller than 10% by weight, the fluidity will be deteriorated and the external appearance of molded articles will be impaired.

(6) Preparation of the Thermoplastic Elastomer Composition

For preparing the thermoplastic elastomer composition of the present invention, the components (A), (B), (C) and (D) may be mixed together in predetermined proportions followed by partial crosslinking. But, preferably, the components (B) and (C) are first mixed together and partially crosslinked, thereafter the remaining components [component (A) and component (D)] are incorporated in the mixture, or the components (B), (C) and (D) are first mixed together and partially crosslinked, thereafter the component (A) is incorporated in the mixture. The above preferable methods may be used to obtain higher fluidity at the same mixing ratio. In such a case, however, strength and heat resistance will be somewhat deteriorated.

The mixing and partial crosslinking may be effected by any known method. A typical example is a mechanical melt-kneading method which is carried out under the addition of a crosslinking agent to the above mixture. according to this known method, the partial crosslinking can be effected using any of uni- and biaxial extruders, Bambury's mixer, various kneaders and rolls. The melt-kneading temperature is generally not higher than 300° C. and preferably it is a temperature at which the half-value period of the crosslinking agent used is not longer than one minute, usually in the range of 100° to 300° C. The partial crosslinking may be performed using heat or radiation after incorporating the crosslinking agent in the mixture by impregnation or any other suitable means.

As the crosslinking agent, an organic peroxide is usually employed. Examples are 2,5-dimethyl-2,5-di(t-butylperoxy)hexane, di-t-butyl peroxide, di(t-butylperoxy)diisopropylbenzene, di(t-butylperoxy)diisobutylbenzene, dicumyl peroxide, t-butylcumyl peroxide, t-butylperoxy benzoate, 1,1-bis(t-butylperoxy)-3,3,5-trimethyl peroxide, benzoyl peroxide, and p-chlorobenzoyl peroxide.

There may be used a crosslinking aid together with the crosslinking agent. Examples are liquid polybutadiene, divinylbenzene, ethylene dimethacrylate, and diallyl phthalate.

The amount of the crosslinking agent used is in the range of 0.005 to 3 wt. %, preferably 0.05 to 1.0 wt. %, provided this range does not always constitute a limitation because the amount of the crosslinking agent to be used is determined according to the performance required for the crosslinked composition. Several kinds of crosslinking agents and crosslinking aids may be used together according to purposes.

The percent insolubles in boiling xylene (gel percentage) which is determined after extracting the thermoplastic elastomer composition of the present invention thus obtained by partial crosslinking, with boiling xylene for 5 hours, is in the range of 0.5 to 60 wt. %, preferably 2 to 50 wt. %. If the gel percentage is smaller than 0.5 wt. %, the heat resistance and the oil resistance will become poor, and a gel percentage exceeding 60 wt. % will result in reduced fluidity and elongation.

Before or after crosslinking, or during crosslinking (particularly during melt-kneading), there may be added, if necessary, fillers such as carbon black, calcium carbonate, silica, metallic fibers and carbon fibers, as well as additives such as antioxidant, flame retardant and coloring agent, and paraffinic, naphthenic or aromatic mineral oils for assisting the dispersion of the fillers and enhancing flexibility and elasticity.

Further, various kinds of resins and rubbers may be added, if necessary, in amounts not causing a change in performance of the thermoplastic elastomer composition of the present invention; for example, crystalline polyolefins such as high and low density polyethylenes and linear low density polyethylenes, natural and synthetic rubbers, and styrene-based thermoplastic elastomers.

The thermoplastic elastomer composition of the present invention has the following characteristics.

(a) Superior in fluidity, so easy to mold, giving molded products having good appearance.

(b) Superior in heat and oil resistance.

(c) Small permanent elongation makes deformation difficult.

(d) Superior in flexibility.

(e) Low density and very light weight.

Since the thermoplastic elastomer composition of the present invention has such excellent characteristics, its application range is extremely wide. The following are application examples thereof:

(a) automobile interior sheet, mud guard, lace and cover

(b) electric wire coating material

(c) components of various electric appliances

(d) hose

(e) various packings

(f) window frame sealing material

(g) sound insulating material

(h) modifier for various polymers

The following examples are given to further illustrate the present invention, but the invention is not limited thereto. In the following working examples and comparative examples, physical properties were measured in the following manner.

[Measurement by DSC]

A hot-pressed 100 μm thick film as a specimen is heated to 170° C. and held at this temperature for 15 minutes, followed by cooling to 0° C. at a rate of 2.5° C./min. Then, from this state the temperature is raised to 170° C. at a rate of 10° C./min and measurement is made. The vertex position of the maximum peak of peaks appearing during the heat-up period from 0° to 170° C. is regarded as the maximum peak temperature (Tm).

[How to Determine Insolubles in Boiling n-Hexane]A 200 μm thick sheet is formed using a hot press, from which are then cut out three sheets each 20 mm long by 30 mm wide. Using these sheets, extraction is made in boiling n-hexane for 5 hours by means of a double-tube type Soxhlet extractor. n-Hexane insolubles are taken out and vacuum-dried (50° C., 7 hours), then the percentage insolubles (C₆ insoluble) in boiling n-hexane is calculated in accordance with the following equation: ##EQU1## [Preparing Test Sheet]

Each resin composition obtained is placed in a mold 2 mm thick, 150 mm long and 150 mm wide, preheated at 210° C. for 5 minutes, then pressure-molded for 5 minutes at the same temperature and at 150 kg/cm², and thereafter cooled for 10 minutes at 30° C. under the pressure of 150 kg/cm², followed by annealing at 50° C. for 20 hours and allowing to stand at room temperature for 24 hours. Thereafter, physical properties are measured.

[Tensile Test]

Test piece is prepared using No. 3 dumbbell in accordance with JIS K 6301 and it is measured for tensile strength at a pulling rate of 50 mm/min.

[Permanent Elongation]

Test piece is prepared using No. 3 dumbbell in accordance with JIS K 6301. It is held at 100% elongated state for 10 minutes, then contracted suddenly and allowed to stand for 10 minutes to check a percentage elongation, from which is determined a permanent elongation.

[Vicat Softening Point]

A 3 mm thick specimen is prepared in accordance with the test sheet preparing method and it is used for measurement. A heat transfer medium is heated at a rate of 50° C./min while applying a load of 250 g through a needle-like indenter placed perpendicularly to the specimen in a heating bath, and the temperature of the heat transfer medium at the time when the needle-like indenter permeated 1 mm is regarded as a Vicat softening point.

[Hardness]

Test piece is prepared in accordance with JIS K 6301 and measured for hardness using type A and type C testing machines.

[Gel Percentage]

A 200 μm thick sheet is prepared using a hot press (at 200° C. for 5 minutes), from which three 40 mm×20 mm sheets are cut out. The three sheets are each placed in a 120-mesh wire gauze bag and extracted in boiling xylene for 5 hours using a double-tube type Soxhlet extractor. Boiling xylene insolubles are taken out and vacuum-dried (80° C., 7 hours) to determine the percentage thereof as a gel percentage.

[External Appearance of Molded Article]

When melt flow rate (MFR) is measured at 230° C. and at 21.6 kg load, the surface condition of an extruded product is observed with the eye.

⊚ very good

○ good

Δ slight bad

X bad

Components (A) to (D) used in Examples and Comparative Examples are as follows:

[Preparation of Components (A-1) and (A-2)]

Ethylene/butene-1 copolymers (A-1) and (A-2) were prepared by copolymerizing ethylene and butene-1 in the presence of a catalyst comprising a solid catalyst component and triethylaluminum, the solid catalyst component having been obtained from a substantially anhydrous magnesium chloride, 1,2-dichloroethane and titanium tetrachloride.

Component (A-1) thus obtained was found to have an ethylene content of 88.3 mol %, a melt index of 0.9 g/10 min, a density of 0.896 g/cm³, a maximum peak temperature according to DSC of 119.8° C. and a boiling n-hexane insolubles content of 82 wt. %.

Component (A-2) thus obtained was found to have an ethylene content of 91.8 mol %, a melt index of 5.0 g/10 min, a density of 0.904 g/cm³, a maximum peak temperature according to DSC of 121.4° C. and a boiling n-hexane insolubles content of 92 wt. %.

[Preparation of Component (A-3)]

Ethylene/butene-1 copolymer (A-3) was prepared by copolymerizing ethylene and butene-1 in the presence of a catalyst comprising a solid catalyst component and triethylaluminum, the solid catalyst component having been obtained from a substantially anhydrous magnesium chloride, anthrathene and titanium tetrachloride.

Component (A-3) thus obtained was found to have an ethylene content of 85.5 mol %, a melt index of 1.0 g/10 min, a density of 0.890 g/cm³, a maximum peak temperature according to DSC of 121.6° C. and a boiling n-hexane insolubles content of 58 wt. %.

[Component (B)]

The characteristics of three polypropylenes (components (B-1), (B-2) and (B-3), respectively) used are as follows:

    ______________________________________                                                                  Ethylene                                                                       Content  Melt Index                                   Component                                                                               Polymerization Method                                                                          (mol %)  (g/10 min)                                   ______________________________________                                         (B-1)    propylene       --       4                                                     homopolymerization                                                    (B-2)    random copolymeri-                                                                             5.9      7                                                     zation with ethylene                                                  (B-3)    block copolymeri-                                                                              5.3      8                                                     zation with ethylene                                                  ______________________________________                                    

[Preparation of Components (C-1) and (C-2)]

Ethylene, propylene and ethylidene norbornene (ENB) were copolymerized using a vanadyl trichlorideethylaluminum sesquichloride catalyst to obtain copolymer rubbers (C-1) and (C-2). Component (C-1) was found to have a Mooney viscosity (ML₁₊₄, 100° C.) of 90, a propylene content of 27 wt. %, a density of 0.863 g/cm³ and an ENB content of 16 in terms of iodine value.

Component (C-2) was found to have a Mooney viscosity (ML₁₊₄, 100° C.) of 47, a propylene content of 25 wt. %, a density of 0.863 g/cm³ and an ENB content of 19 in terms of iodine value.

[Component (D)]

The characteristics of three ethylene/ethyl acrylate copolymers (components (D-1), (D-2) and (D-3), respectively) are as follows:

    ______________________________________                                                     Melt Index                                                                               Ethyl Acrylate Content                                   Component   (g/10 min)                                                                               (mol %)                                                  ______________________________________                                         (D-1)       5         7.0                                                      (D-2)       10        8.4                                                      (D-3)       3         5.0                                                      ______________________________________                                    

EXAMPLES 1-9 AND COMPARATIVE EXAMPLES 1-9

Components (B), (C) and (D) in the proportions stated in Table 1, 0.5 wt. % of di(t-butylperoxy)dipropylbenzene (crosslinking agent), 0.1 wt. % of Irganox 1010 (antioxidant, a product of Ciba Geigy AG) and 0.15 wt. % of calcium stearate (lubricant) were dry-blended and then introduced into a Bambury's mixer preheated to 200° C., in which kneading was performed for 10 minutes at 40 rpm. Then, a predetermined amount of component (A) was added and kneading was performed again at 200° C. for 10 minutes to obtain thermoplastic elastomer compositions. The compositions were measured for physical properties. The results of the measurements are as shown in Table 1 and 2.

In Example 9, 1 wt. % of the crosslinking agent was used.

EXAMPLE 10

Components (B) and (C) in the proportions stated in Table 1, and the same crosslinking agent, antioxidant and lubricant in the same proportions as in Examples 1-9 were dry-blended and then introduced into a Bambury's mixer preheated to 200° C., in which kneading was performed for 10 minutes at 40 rpm. Then, components (A) and (D) in the proportions stated in Table 1 were added and kneading was performed again for 10 minutes to obtain a thermoplastic elastomer composition. The composition was measured for physical properties. The results of the measurement are as shown in Table 1.

EXAMPLE 11

Components (A), (B), (C) and (D) in the proportions stated in Table 1, and the same crosslinking agent, antioxidant and lubricant in the same proportions as in Examples 1-9 were dry-blended and then introduced into a Bambury's mixer preheated to 200° C., in which kneading was performed for 20 minutes at 40 rpm to obtain a thermoplastic elastomer composition. The composition was measured for physical properties. The results of the measurement are as shown in Table 1.

COMPARATIVE EXAMPLE 10

The procedure of Example 11 was repeated except that the crosslinking agent was not added. The results are as shown in Table 2.

COMPARATIVE EXAMPLE 11

The procedure of Example 1 was repeated except that component (A) was replaced by a straight-chain, low density polyethylene (LINIREX AF 2320, a product of Nippon Petrochemicals Co., Ltd., melt index 1.0 g/10 min, density 0.922 g/cm³, DSC maximum peak temperature 122.1° C., boiling n-hexane insolubles content 98.8 wt. %). Physical properties of the resultant composition were measured, the results of which are as set forth in Table 2.

                                      TABLE 1                                      __________________________________________________________________________     Composition           Melt Flow Rate  Tensile                                                                             Tensile                                           Blending Ratio                                                                         230° C., 2.16 kg                                                                230° C., 21.6 kg                                                                Strength                                                                            Elongation                          Example                                                                             Component                                                                               (wt. %) (g/10 min)                                                                             (g/10 min)                                                                             (kg/cm.sup.2)                                                                       (%)                                 __________________________________________________________________________     1    A-1/B-2/C-1/D-1                                                                         25/25/25/25                                                                            2.1     210     115  540                                 2    A-1/B-2/C-1/D-1                                                                         20/30/25/25                                                                            8.4     >300    102  600                                 3    A-1/B-2/C-2/D-1                                                                         22.5/22.5/20/35                                                                        1.8     >300    100  600                                 4    A-3/B-2/C-1/D-1                                                                         15/27.5/27.5/30                                                                        1.6     >300    107  500                                 5    A-1/B-2/C-1/D-2                                                                         27.5/15/27.5/30                                                                        0.8     110     101  560                                 6    A-1/B-3/C-1/D-1                                                                         30/27.5/15/27.5                                                                        4.7     >300    103  360                                 7    A-1/B-2/C-1/D-2                                                                         27.5/30/27.5/15                                                                        0.5     82       91  460                                 8    A-2/B-2/C-1/D-3                                                                         35/15/35/15                                                                            0.6     98      105  610                                 9    A-1/B-2/C-1/D-1                                                                         15/30/20/35                                                                            0.3     65      135  310                                 10   A-1/B-2/C-1/D-1                                                                         35/22.5/22.5/20                                                                        1.7     240     125  420                                 11   A-1/B-1/C-1/D-1                                                                         25/25/25/25                                                                            0.5     140     138  560                                 __________________________________________________________________________          Permanent                                                                            Vicat       Gel   Appearance of                                          Elongation                                                                           Softening                                                                            Hardness                                                                             Percentage                                                                           Extruded Product                                  Example                                                                             (%)   Point (°C.)                                                                   JIS A/C                                                                              (%)   (with the eye)                                                                          Note                                     __________________________________________________________________________     1    19    105.5 84/44 16.8  ⊚                                  2    23    120.3 91/58  1.8  ○                                          3    15     93.9 77/35 10.5  ⊚                                  4    16    101.2 80/41 15.3  ○                                          5    12     96.2 72/33 33.8  ○                                          6    23    11.0  85/52  8.5  ⊚                                  7    18    116.5 82/43 29.5  Δ                                           8    16     98.0 83/41 22.4  ○                                          9    15    122.5 82/45 45.2  ○ crosslinking agent 1%                    10   20    110.3 85/45 19.6  ○                                          11   17    118.3 84/46 20.4  ○                                          __________________________________________________________________________

                                      TABLE 2                                      __________________________________________________________________________            Composition         Melt Flow Rate   Tensile                                                                             Tensile                       Comparative        Blending Ratio                                                                         230° C., 2.16 kg                                                                 230° C., 21.6                                                                   Strength                                                                            Elongation                    Example                                                                               Component   (wt. %) (g/10 min)                                                                              (g/10 min)                                                                             (kg/cm.sup.2)                                                                       (%)                           __________________________________________________________________________     1      A-1/B-2/C-1/D-1                                                                            50/10/20/20                                                                             0.15    18      145  740                           2      A-1/B-2/C-1 25/50/25                                                                               0.6      140      93  360                           3      B-2/C-1/D-1 25/50/25                                                                                0.35    32       53  260                           4      A-1/B-2/D-1 25/25/50                                                                               18       >300    155  820                           5      A-1/B-2/C-1/D-1                                                                            55/20/20/5                                                                             0.1       8      122  590                           6      A-2/B-2/C-1/D-3                                                                             5/30/35/30                                                                            0.2      68       58  290                           7      A-2/B-2/C-1/D-3                                                                            30/10/30/30                                                                             0.05     5       98  450                           8      A-2/B-2/C-1/D-3                                                                            35/30/5/30                                                                             1.5      240     118  560                           9      A-2/B-2/C-1/D-3                                                                            30/35/30/5                                                                             0.2      42      148  570                           10     A-1/B-2/C-1/D-1                                                                            25/25/25/25                                                                            14       >300     85  330                           11     *LLDPE/B-2/C-1/D-1                                                                         25/25/25/25                                                                            2.0      170     130  500                           __________________________________________________________________________            Permanent                                                                            Vicat        Gel   Appearance of                                  Comparative                                                                           Elongation                                                                           Softening                                                                            Hardness                                                                              Percentage                                                                           Extruded Product                               Example                                                                               (%)   Point (°C.)                                                                   JIS A/C                                                                               (%)   (with the eye)                                                                          Note                                  __________________________________________________________________________     1      19    75.0  93/57  19.6  ○                                       2      35    128.4 > 100/85                                                                               4.5  X        Component (D) was not used            3      14    78.0  75/33  17.7  Δ  component (A) was not used            4      28    82.8  >100/78                                                                                0.5  ⊚                                                                        component (C) was not used            5      30    81.0  98/65  36.5  X                                              6      17    101.5 84/40  18.2  ○                                       7      14    69.2  78/38  24.5  ○                                       8      35    118.5 >100/88                                                                               22.5  ⊚                               9      18    109.0 88.56  33.0  X                                              10     24    52.0  82/40        ○ crosslinking agent was not used       11     27    77.0  >100/70                                                                               13.0  ○                                       __________________________________________________________________________      *LLDPE: linear low density polyethylene                                   

What is claimed is:
 1. A thermoplastic elastomer composition prepared by partially crosslinking a composition comprising the following components (A), (B), (C) and (D):(A) 10-40% by weight of an ethylene/α-olefin copolymer prepared by copolymerizing ethylene and an α-olefin having 3 to 12 carbon atoms in the presence of a catalyst comprising a solid component and an organoaluminum compound which solid component contains at least magnesium and titanium, said ethylene/α-olefin copolymer having the following properties (I) to (IV):(I) Melt index: 0.01-50 g/10 min (II) Density: 0.860-0.910 g/cm³ (III) Maximum peak temperature as measured according to a differential scanning calorimetry (DSC): not lower than 100° C. (IV) Insolubles in boiling n-hexane: not less than 10 wt. % (B) 15-35% by weight of a propylene polymer; (C) 10-40% by weight of an ethylene/α-olefin copolymer rubber; and (D) 10-40% by weight of an ethylene/unsaturated monocarboxylic acid ester copolymer in which the carboxylate unit content is 2-10 mol %.
 2. A composition as set forth in claim 1, wherein the propylene polymer (B) is a homopolymer of propylene or a copolymer of propylene and less than 30% by weight of an α-olefin having 2 to 8 carbon atoms.
 3. A composition as set forth in claim 1, wherein the melt flow rate of the propylene polymer (B) is in the range of 0.01 to 100 g/10 min.
 4. A composition as set forth in claim 1, wherein the ethylene/α-olefin copolymer rubber (C) has a Mooney viscosity (ML₁₊₄, 100° C.) in the range of 10 to
 95. 5. A composition as set forth in claim 1, wherein the unsaturated monocarboxylic acid ester of the the ethylene/unsaturated monocarboxylic acid ester is an ester of acrylic acid or methacrylic acid with an alcohol having 1 to 6 carbon atoms. 